Gas turbine engines are used in myriad systems and environments. For example, gas turbine engines are used in various types of aircraft and watercraft, and in numerous industrial systems and environments. In each of these exemplary systems and environments, gas turbine engines may be used to supply propulsion power, to generate electrical power, or both. No matter its specific end-use, a gas turbine engine typically includes a combustor, a power turbine, and a compressor. During operation, the compressor draws in ambient air, compresses it, and supplies compressed air to the combustor. The combustor receives fuel from a fuel source and the compressed air from the compressor, and supplies high energy combustion gas to the power turbine, causing it to rotate. The power turbine includes a shaft that may be used to drive the compressor. Moreover, depending upon the particular end-use, the turbine may additionally drive a generator, a turbo fan, or a shaft that drives a power source.
In addition to its potentially myriad uses, a gas turbine engine may also be exposed to numerous and varied environmental conditions. For example, a gas turbine engine may be exposed to relatively high altitudes, adverse weather conditions, or numerous other conditions that may result in operation below freezing temperatures. During operations below freezing, ice formation may occur at various locations on or within the gas turbine engine. The gas turbine engine inlet is particularly prone to ice formation during such freezing conditions. Not surprisingly, excessive ice formation and accumulation, or the ingestion of ice into the inlet, can adversely affect gas turbine engine performance and/or have various other deleterious effects on gas turbine engine components.
In particular, it is generally known that the operating efficiency of a gas turbine is at least partially dependent upon the axial clearance or gap between rotor blade tips and the shroud. If the axial clearance between the rotor blade tips and the surrounding shroud is too large, additional flow may leak through the gap between the rotor blade tips and the surrounding shroud, decreasing the turbine's efficiency. Conversely, if the axial clearance is too small, the rotor blade tips may strike the surrounding shroud during certain turbine operating conditions. It is also generally known that axial clearances may change due, among other factors, to relative thermal growth between the rotating rotor and stationary shroud. During periods of such differential thermal growth, clearance between the moving blade tips and the stationary shroud may occur. Since components of turbines and other rotating machines are, in many instances, made of different materials with different thicknesses, such components exhibit different rates of thermal growth from a cold startup condition to steady state operating condition and during transient operating conditions.
To facilitate optimizing turbine efficiency, various clearance management tools and/or design methodologies may be used to attain a balanced design that provides relatively tight operating clearances, yet avoids potential rubbing during transients and/or during operations at off-design conditions and/or that may result from differential thermal growth. Various anti-ice formation devices presently known do not provide adequate thermal isolation to differential thermal growth.
Hence, there is a need for a device and system that prevents, or at least substantially prevents, ice formation and accumulation on a gas turbine engine inlet and/or ice ingestion into a gas turbine engine inlet, and that does not adversely impact axial clearances within the engine. The present invention addresses at least this need.